The present invention relates to a method and apparatus for processing staple fibers on a roller card unit of the type provided with a main cylinder and associated pairs of work and clearing rollers.
The output level of a card unit is limited by various factors including particularly the type of fibers to be processed, the degree of separation of the fiber material coming into the card unit, the percentage of waste material in the fibers, the desired quality of the resulting web, the configuration of the cylinder card clothing and the so-called C value of the main cylinder. Optimum setting of the rollers with respect to one another is a prerequisite. The C value, which constitutes the load factor for the cylinder card clothing, must be selected in dependence on the previously mentioned factors.
The carding process which takes place between the work rollers and the main cylinder requires, as a prerequisite for achieving the desired results that the optimum relative speed exist between the work rollers and the main cylinder. This speed depends on the type and length of the fibers.
If it is assumed that the peripheral speed of the main cylinder is adjustable and can be varied between 600 and 1500 m/min, and the peripheral speed of the work rollers can be varied between 5 and 25 m/min, the processing location produces a variation range for the peripheral speed differential of between 24 and 300 times, the two rollers rotating in the same direction.
If it is assumed that the main cylinder always operates with an optimum C value, the work rollers may be loaded very heavily with fibers. This is so because, as mentioned above, the peripheral speed of the work rollers can be varied only between quite defined limits in dependence on the type and length of the fibers. If these limits are exceeded, too many fibers will arrive at the clearing rollers, which rotate with a constant peripheral speed. This again leads to excess quantities of fibers between the clearing rollers and the main cylinder and thus to a poor web quality.
Poor web quality in high production output installations where the work rollers are too heavily loaded with fibers may also have its origin in the fact that the clearing rollers remove the fiber fleece from the work rollers in batches and feed it to the main cylinder in the same manner. This then results in a final fiber web which is fleecy, or cloudy.
In the above-mentioned exceptional cases, there exists the possibility of increasing the peripheral speed of the work rollers, when they rotate in a direction such that their peripheries advance in the same direction as the periphery of the main cylinder at the work location in question so that the condensing ratio between the work rollers and the main cylinder is reduced down to 1:6. The condensing ratio is the value given by the ratio "peripheral speed of the work rollers/peripheral speed of the main cylinder".
In that case the work rollers carry fewer fibers per unit area but the amount of material put through on the work rollers will nevertheless correspond to the high production output of the card unit. The peripheral speed of the work rollers can be changed in such cases so that the ratio to the peripheral speed of the clearing rollers can be set to a value of 1:1 and even lower. The clearing rollers can then take over a relatively fine and closed fiber web from the work rollers and feed it to the main cylinder.